Battery configs for cree/luxeon DIY bike lights



D

dej

Guest
Gday,
Just a question for those who have made their own lights using luxeons
or cree powerleds..
(or other nerdy types who like soldering stuff)

I built up a light using 3 cree xr-e power leds. At first i just got 4
AA 2500mah rechargeables and put them in a battery case from jaycar.
The case meant the batteries were wired in series. So i ended up with
4.8v and 2500mah.
The light was incredibly bright, (much more so than my 12watt marwi
nightpro halogen) but it'd last about 10 minutes before starting to
dim

Since then i got some c size 3000mah batteries with solder tabs and
wired them in parallel. Long run times now, but its about as bright as
a standard 30$ led light and useless for the dirt crits (as i found
last night)

So has anyone found a good battery config for ~1-2 hour runtimes with
a fairly small battery pack?
I was thinking of doing a series/parallel wiring config and get the
voltage up to 4.8 and then add 2 more batteries in parallel to
increase the mah

Please excuse my electronics ignorance:)

ps, having 4 months off racing is not cool:(
 

ghostgum

New Member
Aug 30, 2005
245
0
0
dej said:
Gday,
Just a question for those who have made their own lights using luxeons
or cree powerleds..
(or other nerdy types who like soldering stuff)

I built up a light using 3 cree xr-e power leds. At first i just got 4
AA 2500mah rechargeables and put them in a battery case from jaycar.
The case meant the batteries were wired in series. So i ended up with
4.8v and 2500mah.
The light was incredibly bright, (much more so than my 12watt marwi
nightpro halogen) but it'd last about 10 minutes before starting to
dim

You need a current regulator. Suggestions are the BuckPuck or the bFlex controller. I bought a BuckPuck from Cutter Electronics, but they are sure to be available from other places also.

Given that you are actually get 3 white LEDs to illuminate off 4.8V, you must have the LEDs connected in parallel. We can do a quick calculation to work out how much current is through the LEDs. 2500mAH means you can get 2500mA for one hour. Given that you got 10 minutes, you must be pulling about 6 times this, or 15A. Split between 3 LEDs makes it about 5A per LED. They are rated for 1A, so your LEDs will have a very short life when run like that. In practice the current will probably be a bit less, because when you discharge batteries at such a high rate you get less than the rated capacity, so maybe it's only 2-3 amps, but still way too much. The only reason the LEDs have already fried is the battery case. The contact resistance of the battery case will limit the amount of current, which is bad for efficiency. The cells also tend to jump out of the battery case when you go over bumps. Better to buy the solder tab variety of cells (can be bought at Jaycar) and solder then duct tape up your own battery.

Forward voltage for those LEDs is about 3.1V and 350mA, and 3.7V at 1A. With three in series that's about 11.1V. With a BuckPuck you would need about 13.1V from your battery, or 10-11 cells. I'm planning to use 3 XR-E LEDs in series, but I've select the three and the forward voltage is about 3.3V each at 700mA, and I'll run it from 10 x 2500mAH AA NiMH cells.

If you want to run it from about 6V, then I suggest you look at the bFlex controller. I've never used it.
http://www.cutter.com.au/proddetail.php?prod=cut750
The controller costs as much as the 3 XR-E LEDs.

If we assume that you are using 4.8V x 2500mAH battery, and that each LED is running at 700mA, then we can work out the run time.
Power into LEDs = 0.7A * 3.5V * 3 = 7.35W
Efficiency of regulator = 85%, so power out of batter = 7.35 / 0.85 = 8.6W.
Energy stored in battery is 4.8 x 2.5 Watt hours = 12 WH.
So run time is 12 / 8.6 = 1.4 hours.
You can do the maths for your other battery.

My light designs are at
http://www.ghostgum.com.au/misc/BikeLight.htm
 
D

Duncan

Guest
On Aug 10, 11:34 am, dej <[email protected]> wrote:
> Gday,
> Just a question for those who have made their own lights using luxeons
> or cree powerleds..
> (or other nerdy types who like soldering stuff)
>
> I built up a light using 3 cree xr-e power leds. At first i just got 4
> AA 2500mah rechargeables and put them in a battery case from jaycar.
> The case meant the batteries were wired in series. So i ended up with
> 4.8v and 2500mah.
> The light was incredibly bright, (much more so than my 12watt marwi
> nightpro halogen) but it'd last about 10 minutes before starting to
> dim
>
> Since then i got some c size 3000mah batteries with solder tabs and
> wired them in parallel. Long run times now, but its about as bright as
> a standard 30$ led light and useless for the dirt crits (as i found
> last night)
>
> So has anyone found a good battery config for ~1-2 hour runtimes with
> a fairly small battery pack?
> I was thinking of doing a series/parallel wiring config and get the
> voltage up to 4.8 and then add 2 more batteries in parallel to
> increase the mah
>
> Please excuse my electronics ignorance:)
>
> ps, having 4 months off racing is not cool:(


Are you using a constant current source.. what current are you driving
them at?

3x xr-e's at full tilt will consume 3000mAh at 3.7V forward voltage,
so you should get about an hour out of your cells with a reasonable
switchmode supply.. you'll only get 40 minutes or so out of them with
a simple current-limiting resistor.

Don't run tham at 1A.. you'll probably be plenty bright enough at
350mA each, and get about 2hours run time.

I've got a 3W luxeon white front in series with 3xparallel 1W red
(rear) all running off a 750mA powerpuck driver. I had to use
6x2000mAh AA cells to get the voltage high enough for this
configuration (forward voltage of white + the three parallel reds),
but I get something like 2hours run time, which is what I'd expect.
 
O

OzCableguy

Guest
"dej" <[email protected]> wrote in message
news:[email protected]
> So has anyone found a good battery config for ~1-2 hour runtimes with
> a fairly small battery pack?
> I was thinking of doing a series/parallel wiring config and get the
> voltage up to 4.8 and then add 2 more batteries in parallel to
> increase the mah
>


Maybe have a chat with Chervy - http://www.mtbdirt.com.au/chervy/. I'm sure
he could put something together for you or at least point you in the right
direction.
His latest Mk3's use cree emitters but still with the same battery packs I
believe, which are just 3 x Ni-Mh AA batteries which give approx 2hrs of
burn time. The beauty with using Ni-Mh batteries is you can just buy a jumbo
pack for an event and not have to worry about recharging.

I bought a set of luxeon ayups (http://www.ayup.com.au/) which use lithium
batteries with either a 3 or 6 hr burn time. The 3hr one is slightly bigger
than a match box, weighs just 70 grams and velcros straight onto the helmet.
You don't really notice it's there it's so light.
They also have cree lights due out in a couple of weeks and also a low beam
switch later in the year which will double the burn times. They're saying
1000 lumen for the crees and at around $400 for the kit it certainly makes
HIDs and other LED lights less attractive.

--
www.ozcableguy.com
www.oztechnologies.com
 
D

dej

Guest
On Aug 10, 12:08 pm, "OzCableguy" <[email protected]>
wrote:
> "dej" <[email protected]> wrote in message
>
> news:[email protected]
>
> > So has anyone found a good battery config for ~1-2 hour runtimes with
> > a fairly small battery pack?
> > I was thinking of doing a series/parallel wiring config and get the
> > voltage up to 4.8 and then add 2 more batteries in parallel to
> > increase the mah

>
> Maybe have a chat with Chervy -http://www.mtbdirt.com.au/chervy/. I'm sure
> he could put something together for you or at least point you in the right
> direction.
> His latest Mk3's use cree emitters but still with the same battery packs I
> believe, which are just 3 x Ni-Mh AA batteries which give approx 2hrs of
> burn time. The beauty with using Ni-Mh batteries is you can just buy a jumbo
> pack for an event and not have to worry about recharging.
>
> I bought a set of luxeon ayups (http://www.ayup.com.au/) which use lithium
> batteries with either a 3 or 6 hr burn time. The 3hr one is slightly bigger
> than a match box, weighs just 70 grams and velcros straight onto the helmet.
> You don't really notice it's there it's so light.
> They also have cree lights due out in a couple of weeks and also a low beam
> switch later in the year which will double the burn times. They're saying
> 1000 lumen for the crees and at around $400 for the kit it certainly makes
> HIDs and other LED lights less attractive.
>
> --www.ozcableguy.comwww.oztechnologies.com


Thanks for all the info guys!
will check it all out when i get home and have time to read it all..
I forgot to mention that i'm using 2 micropuck drivers (wired in buck/
puck) configuration
I got all the stuff from cutter electronics and just followed some
instructions from the following:
http://www.racedaynutrition.com/features/bikelight.aspx
The only thing not mentioned in that site is what battery config they
used
 
D

Duncan

Guest
dej,

please check out http://www.leddynamics.com/LuxDrive/datasheets/Micro_Puck_App_Note.pdf

If you ran the system in boost configuration (page 2) with > Vf (LED
forward voltage, about 3.7V @ 1A) input, then you're running the LED's
at a very high unregulated current: hence the short burn time (very
impressed it wasn't burn-out).

If you run in boost config (as suggested by the page you linked, see
page 5 of application note), you need an input voltage from 1 to 3V. I
suggest 2 cells in series for 2.4V would be the thing to use.

Alternatively, you can wire buck/boost as per page 6 of the
application note with an input voltage anywhere from 1 to 7V... this
is slightly less efiicient, though.

rgds

duncan
 

ghostgum

New Member
Aug 30, 2005
245
0
0
dej said:
I forgot to mention that i'm using 2 micropuck drivers (wired in buck/
puck) configuration
I got all the stuff from cutter electronics and just followed some
instructions from the following:
http://www.racedaynutrition.com/features/bikelight.aspx
The only thing not mentioned in that site is what battery config they
used

Note Duncan's comment that the battery voltage (you say 4.8V) must be less than the LED voltage (3.7V). It appears yours is not, so the boostpuck won't regulate. Very bright LEDs, very short life.

Given that you are already have the 2009 Micropuck, I would
suggest using 2 x NiMH cells (nominally 2.4V) as input which drive one LED. Then use the second Micropuck to drive two LEDs in series (not certain that this will work correctly). Switch the two micropucks separately. The Micropuck datasheet says maximum input voltage is 3V. Your 4.8V is too high.

If you need to connect cells in parallel to get enough capacity, only do it when the both have the same terminal voltage. That is, connect two fully charged cells together, or two flat cells together, but don't connect one full and one empty cell together unless you want to melt the wire connecting the two, or possibly make a cell explode (less likely).

If you are using the same design as the referenced article, then you are running in boost mode and will have this problem. The solution may be to put the 3 LEDs in series and remove the switch.

I'd get a digital multimeter with 10A current range and measure the current through each LED, and also the voltage across each LED. Then you can work out how much power each is consuming, and match that against the rated battery capacity and run time.

Be careful using the current range on the meter. You usually want to wire it in before turning on the power. Then as soon as you have finished with the current measurement, move the lead back onto the V/ohm input of the meter. Accidently using using the V input to measure current doesn't work and doesn't damage the meter. Accidently using the A input to measure voltage can destroy the meter.